diff --git a/sklearn/ensemble/iforest.py b/sklearn/ensemble/iforest.py
index 8a1bd3625..f513c06f9 100644
--- a/sklearn/ensemble/iforest.py
+++ b/sklearn/ensemble/iforest.py
@@ -120,6 +120,11 @@ class IsolationForest(BaseBagging, OutlierMixin):
     verbose : int, optional (default=0)
         Controls the verbosity of the tree building process.
 
+    warm_start : bool, optional (default=False)
+        When set to ``True``, reuse the solution of the previous call to fit
+        and add more estimators to the ensemble, otherwise, just fit a whole
+        new forest. See :term:`the Glossary <warm_start>`.
+
 
     Attributes
     ----------
@@ -170,6 +175,7 @@ class IsolationForest(BaseBagging, OutlierMixin):
                  contamination="legacy",
                  max_features=1.,
                  bootstrap=False,
+                 warm_start=False,  # Expose warm_start parameter
                  n_jobs=None,
                  behaviour='old',
                  random_state=None,
@@ -181,6 +187,7 @@ class IsolationForest(BaseBagging, OutlierMixin):
                 random_state=random_state),
             # here above max_features has no links with self.max_features
             bootstrap=bootstrap,
+            warm_start=warm_start,  # Pass warm_start to the superclass
             bootstrap_features=False,
             n_estimators=n_estimators,
             max_samples=max_samples,
